PETpla.net Insider 06 / 2018

MATERIALS / RECYCLING PET planet Insider Vol. 19 No. 06/18 www.petpla.net 19 Circular Economy of PET waste by loop recycling Dream, fiction or reality? by Dr. Ulrich Thiele, Polyester Technology During the past 20 years the polyester recycling industry has grown to become a multimillion-ton business; it enjoys an above-average growth that continues today. According to recent publications the amount of PET recycled in 2017 was about 10 million tons. Most of this rPET is generated by mechanical recycling processes, in which PET bottles are collected, intensively sorted, cleaned, ground and then converted, either to polyester intermediates or re-pelletised. There have been many attempts to establish chemical recycling processes on an industry-scale, with the target of producing PTA or BEHT and MEG from polyester waste during the past 10 years. Some of the more recent developments are described below. 1. New chemical recycling processes under development A relatively small portion of PET bottle waste (less than 5%) is con- verted by means of chemical recy- cling back to polyester raw materials: PTA (Purified Terephthalic Acid) and MEG (Mono Ethylene Glycol). Patent literature has a large number of pat- ents dealing with the chemical PET recycling, mainly based on hydroly- sis to produce PTA, and glycolysis to produce BEHT or methanolysis to produce DMT. Hussain Al Ghatta of former M&G group developed a process whereby PET waste is hydrolysed by concentrated acetic acid under pres- sure, to generate PTA and MEG. The advantage of this process is the fact that the resulting terephthalic acid is dissolved in acetic acid, which is then diluted with water as the medium of further purification and trans-crystalli- sation. Unfortunately, the process did not go beyond the pilot stage. For full details see: US2002077500 (A1) ― 2002-06-20 “Recovery of dicarboxylic aromatic acids from polyester-resin contained in articles for recycling”. In 2005, Fraunhofer developed the “Crea Solve” process. The key step of this technology is the use of a blend of selective solvents to dis- solve the PET waste, with removal of impurities by filtration, precipita- tion by a non-solvent and separation of the purified polyester. The inven- tion relates to a method for recycling polyesters or polyester mixtures from polyester-containing waste. Accord- ing to this method, the polyester or polyester mixture is dissolved in a sol- vent, whereupon free-flowing particles thereof are precipitated with the aid of a precipitating agent. The precipitating agent is selected so that the precipi- tating agent and the solvent can later be separated in a simple manner. This process has not progressed beyond pilot stage up till now. Canadian company Loop Indus- tries recently published a new PET recycling process on its website, based on solvent supported alkaline hydrolysis of PET waste. The publica- tion made public that Loop Industries is investigating this process along with Danone and Coca-Cola. Inten- sive public patent research brought the result that this process is most likely based on the invention of Hatem Essaddam, inventor of PET US Appl. 20170008826 and 20170152203, and USP 9,550,713, dated 27.01.2017. At the heart of this process is the treat- ment of PET flakes with a solvent mix- ture of methanol and dichlorometh- ane, in the presence of equimolar amounts of potassium hydroxide. Provided the input material is stand- ard bottle PET, the resulting solution contains terephthalic acid 2-4% isoph- Mechanical vs. chemical recycling: The figure illustrates the complexity of the chemical process, with the most important being that the raw materials produced by recycling have to be reconstituted into polymers. RECYCLING S P E C I A L